v1.39 cliking on product url from cart, why products attributes not be remembered ?

[inception]

for the zen cart 1.39h, if you add the product with attributes to shopping cart, then from the shopping_cart page, click on the product url, the url is like this
xxxxxxxxxx29:ab2xxxxxxxxxxxxxxxx
it takes you back to the product info page and all the attributes selected are remembered.

but why my product url on shopping cart page is without
:ab2xxxxxxxxxxxxxxxx
it just takes me to the product info page, no attributes remembered.

what do i miss? which files should i check? any ideas?

[schoolboy]

The attributes ARE remembered for the product already in the cart.

It does not make sense to "toggle" this behaviour.

Here's why.

I buy a pair of SHOES that are available in BROWN and BLACK and sizes 7 , 8 , 9 .

So... my first choice is BROWN size 7.

But I really like that style of shoe, so I also want a BLACK pair. I go back to the product info screen, and then choose a size 7 in BLACK.

If the "toggle" effect was there, I would be FORCED to buy another pair in BROWN.

[inception]

yes, sounds reasonable,
to remember attributes when cliking back on the product url is not so important for my site, i guess enable to modify the options is better.

but i find almost all other sites which running 1.39 get this function, i'm not sure if it cause by installing one other mod,
so i want to find out that mod which's in conflict with this function to avoide the hidden trouble

i dont know which files should i check firstly, i have installed many mods